After devices or circuits are fabricated on a semiconductor wafer, the individual devices or circuits are usually separated from each other by sawing using a diamond-impregnated saw blade or by scribing the wafer with a scribe tool and fracturing the wafer along the scribed lines. In certain types of devices or semiconductor materials, scribing and cleaving is the preferred method of separating the individual units of the semiconductor wafer.
In order to scribe a semiconductor wafer, the scribe tool is placed on the surface of the wafer near the distal edge of the wafer and the wafer and scribe tool are moved laterally relative to each other for a distance equal to the entire width of the wafer, forming a scribe line. The scribe tool is raised from the surface of the wafer and the scribe tool and the wafer are indexed relative to each other in the direction perpendicular to the scribe line for a distance equal to the width of an individual device. The scribe tool is again placed on the surface of the wafer and the wafer and scribe tool are moved laterally relative to each other again for a distance equal to the entire width of the wafer forming a second scribe line. This process continues until the proximal edge of the wafer surface is reached. The wafer is then rotated 90 degrees and the process described above is repeated.
One of the most important process parameters in achieving a successful scribe line in the surface of the wafer, which in turn results in a successful cleave, is the scribe force applied to the scribe tool. If the force applied to the semiconductor wafer surface by the scribe tool is too low, the stress created in the semiconductor material under the scribe line is insufficient to allow a successful cleave during the breaking step. If the force applied to the semiconductor wafer surface by the scribe tool is too high, the surface of the semiconductor material will fracture and crack resulting in excessive chip out of material along the scribe line and possibly cracking that extends into the active regions of the semiconductor device.
Several different approaches have been employed in an effort to control the scribe force in different scribe apparatus. U.S. Pat. No. 3,094,785 discloses the approach of using changeable weights acting on a scribe arm that in turn applies force to the scribe tool. U.S. Pat. No. 4,502,225 discloses use of a series of levers and springs to apply the scribe force. Other known apparatus use air pressure acting on the scribe arm to control the scribe force. U.S. Pat. No. 5,820,006 describes a method of electronically controlling the scribe force by using a load cell mounted in a voice coil. Since load cells are analog devices, this approach will not work well, as the electrical noise from the motor drive system will interfere with the analog output from the load cell. U.S. Pat. No. 6,826,840 describes apparatus and a method to improve the control of force applied to the surface of a semiconductor wafer by the scribe tool using flexures and a linear encoder.